1. Field of the Invention
This invention lies in the field of surface treated plastic web members (including films and laminates), particularly such structures which have a pattern created in surface portions thereof which is achieved as a direct result of charge treatment.
2. Prior Art
To enhance yields of a cook-in packaged meat product and particularly so as to minimize and even substantially prevent cook-out of fluids from meat package in a plastic container wherein the meat is cooked, it has been heretofore appreciated that a flexible plastic container can be used which is conformable to the meat product contained therein and whose inside wall portions are meat adherent during cook-in. The container itself can either be of the stuffable type wherein meat is initially compacted against the walls of a somewhat resilient container member such as a casing or the like or the container employed displays heat shrinkable characteristics such that the container particularly at cook temperatures displays a capacity to heat shrink, thereby bringing the container in its sealed configuration into a close conforming condition relative to the meat contained therein so that meat configuration changes during the cook-in process are compensated for by the container shrink characteristics during cooking.
For example, Thompson U.S. Pat. No. 4,411,919 describes the cook-in of packaged meat using an energetic radiation treated, meat adherent inner container surface comprised of a polymeric olefin, while Schirmer U.S. Pat. No. 4,606,922 teaches the use of an irradiation treated ionomer layer as the meat adherent inside surface for a meat cook-in container.
Such meat adhering cook-in packaging techniques, particularly in certain use circumstances, display certain disadvantages. For one thing, when the meat package utilizes meat having a retained skin, such as turkey or other poultry meat, the meat adherent interior surface can be so aggressively adherent to the skin as to result in undesirable delamination and separation of the skin from the cooked meat at the time when the package is removed from the meat following cook-in. Thus, even though the problem of purge or cook-out of fluids has been overcome, the resulting separation of skin from meat is considered to be commercially disadvantageous.
Another problem in the cook-in packaging art involving a plastic container lies in the circumstance that it is difficult, and apparently in some cases apparently presently impossible, to correlate the amount of irradiation or corona treatment or even ozone treatment uniformly given to a plastic surface with the subsequent degree of meat or other high protein material adherence thereto. In other words, the degree or extent of meat adherence, at the present time, does not appear to be regulatable by the amount of uniform surface treatment which is preliminarily given to the meat contacting surface portions of the intended cook-in container to be used for meat processing (preferably without purge).
Another problem in the cook-in packaging art is that uniform surface treatment of the intended interior surface portions of a cook-in container, which treatment is carried out for the purpose of improving the capacity of highly proteinaceous foods to adhere thereto, appears to detract from the ability of the treated surface to adhere by heat sealing to similarly treated surfaces of plastics having even an identical composition. This is important because filled cook-in plastic containers are typically sealed before being exposed to cooking temperatures by heat sealing adjacent inner wall surface portions together. Since steam pressures within the sealed container can develop, for example, in the cooking of beef at about 200.degree. F., unless durable container seals are formed, they tend to open during cooking with undesirable effects. Where the interior surface portions are treated with corona discharge, gamma radiation, ozone, etc., slight alteration in treated surface composition results. The chemical nature of this alteration is not known, but is believed to involve at least some oxidation (perhaps partially oxidized) surfaces brought together and heat sealed, the resulting seal tends to be weaker than a corresponding seal formed between untreated surfaces. This effect thus presents a problem in providing containers for cook-in of meat and other highly proteinaceous foods when the container inside walls are to be adherent to such foods in order to achieve, for example, a purgefree cooked-in product package.
There is a need in the art for new and improved meat adherent surfaces for use in containers adapted for employment in the cook-in meat packaging field.